Messages
Create a Message
BetaMessage beta().messages().create(MessageCreateParamsparams, RequestOptionsrequestOptions = RequestOptions.none())Count tokens in a Message
BetaMessageTokensCount beta().messages().countTokens(MessageCountTokensParamsparams, RequestOptionsrequestOptions = RequestOptions.none())Models
A file download that finished during this call, reported with the
same download_id as its download_started — or without a prior
download_started, when the download finished during the call that
started it (at most one state change per download_id per result).
A file download that finished during this call, reported with the
same download_id as its download_started — or without a prior
download_started, when the download finished during the call that
started it (at most one state change per download_id per result).
tab_id is the caller-assigned identifier for the tab; title and
url describe the page the tab is currently showing and may be empty
strings (a blank tab legitimately has both empty). active marks the
tab that is active after this call; whenever tabs is non-empty,
exactly one entry is marked.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
Per-member configuration for browser_toolset_20260801: one
optional field per member tool, keyed by the member name — the same
name the member's tool_use blocks carry. Every member is an
accepted key, and a member's defaults apply wherever its key is
absent. Unknown keys are rejected: the field set is this toolset
version's complete member set.
Per-member configuration for browser_toolset_20260801: one
optional field per member tool, keyed by the member name — the same
name the member's tool_use blocks carry. Every member is an
accepted key, and a member's defaults apply wherever its key is
absent. Unknown keys are rejected: the field set is this toolset
version's complete member set.
Per-member configuration for browser_toolset_20260801: one
optional field per member tool, keyed by the member name — the same
name the member's tool_use blocks carry. Every member is an
accepted key, and a member's defaults apply wherever its key is
absent. Unknown keys are rejected: the field set is this toolset
version's complete member set.
Per-member configuration for browser_toolset_20260801: one
optional field per member tool, keyed by the member name — the same
name the member's tool_use blocks carry. Every member is an
accepted key, and a member's defaults apply wherever its key is
absent. Unknown keys are rejected: the field set is this toolset
version's complete member set.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.
Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.
Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.
Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.
Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.
Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
Users should round-trip these blocks from responses to subsequent requests to maintain context across compaction boundaries.
When content is None, the block represents a failed compaction. The server treats these as no-ops. Empty string content is not allowed.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
The computer toolset: a single tools[] entry (carrying no
name) that declares the computer tool family. The model is
served the family's tool with any members disabled via configs
removed from its schema. Every member is enabled by default, zoom
included. The single-tool options display_number and
enable_zoom are not fields of a toolset entry — it carries only
type, configs, and cache_control; zoom is controlled
via configs.zoom.enabled.
The computer toolset: a single tools[] entry (carrying no
name) that declares the computer tool family. The model is
served the family's tool with any members disabled via configs
removed from its schema. Every member is enabled by default, zoom
included. The single-tool options display_number and
enable_zoom are not fields of a toolset entry — it carries only
type, configs, and cache_control; zoom is controlled
via configs.zoom.enabled.
Per-member configuration for computer_toolset_20260801: one
optional field per member tool, keyed by the member name — the same
name the member's tool_use blocks carry. Every member is an
accepted key, and a member's defaults apply wherever its key is
absent. Unknown keys are rejected: the field set is this toolset
version's complete member set.
Per-member configuration for computer_toolset_20260801: one
optional field per member tool, keyed by the member name — the same
name the member's tool_use blocks carry. Every member is an
accepted key, and a member's defaults apply wherever its key is
absent. Unknown keys are rejected: the field set is this toolset
version's complete member set.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
The id (msg_...) from this client's previous /v1/messages response. The server compares that request's prompt fingerprint against this one and returns diagnostics.cache_miss_reason when the prompt-cache prefix could not be reused. Pass null on the first turn to opt in without a prior message to compare.
The id (msg_...) from this client's previous /v1/messages response. The server compares that request's prompt fingerprint against this one and returns diagnostics.cache_miss_reason when the prompt-cache prefix could not be reused. Pass null on the first turn to opt in without a prior message to compare.
One block appears per hop where a preceding model actually ran this turn and
declined. A turn where no preceding model ran and declined has no such
boundary and carries no block — the signal for whether a fallback model
served the response is the presence of a fallback_message entry in
usage.iterations, not this block.
The block is treated like a server-tool content block for streaming: it
arrives via the standard content_block_start / content_block_stop
pair and carries no deltas.
Accepted in messages[].content and not rendered into the prompt; not
validated against the request's fallbacks chain or top-level model.
Echo the assistant turn back verbatim, including this block in its original position. The block marks the boundary between content produced before and after a fallback hop, and the server relies on that boundary to validate the turn: when thinking runs flank the boundary, omitting the block merges them into one span the server cannot validate (the request is rejected), and moving it into the middle of a single run is likewise rejected; between non-thinking blocks the block's placement has no validation effect.
A closed enum; additions to the redemption-check vocabulary arrive as deliberate schema updates.
Present exactly when reason is variant_fields_present — never null,
never an empty array; absent otherwise. Fields are named only from your own request, and only after
the sealed variant hash matched. A served best-effort retry has already
been billed at normal price; nothing redeems retroactively, but a corrected
re-send inside the token's five-minute window can still redeem.
Requires anthropic-beta: fallback-credit-2026-07-01; without that
header the field accepts the bare string only. The bare string and the
mode-less object are equivalent (both select strict), so wrapping
an existing token changes nothing by itself.
How a failing token affects the retry. strict (the default, and the bare-string behavior): a failing redemption is a 400 and the retry is not served. best_effort: the retry is served either way — a token-layer failure no longer rejects the request; the retry proceeds at normal price and the outcome is reported on the response's usage.fallback_credit. Two failures stay hard in both modes: a malformed token, and combining fallback_credit_token with fallbacks.
How a failing token affects the retry. strict (the default, and the bare-string behavior): a failing redemption is a 400 and the retry is not served. best_effort: the retry is served either way — a token-layer failure no longer rejects the request; the retry proceeds at normal price and the outcome is reported on the response's usage.fallback_credit. Two failures stay hard in both modes: a malformed token, and combining fallback_credit_token with fallbacks.
See models for additional details and options.
See models for additional details and options.
The request could enable cyber harm, such as malware or exploit development. Benign cybersecurity work can also trigger this category.
The request could enable biological harm, such as dangerous lab methods. Beneficial life sciences work can also trigger this category.
The request could assist the development of competing AI models, which is restricted under Anthropic's commercial terms. Benign machine learning work can also trigger this category.
The request asks the model to reproduce its internal reasoning in the response text. To get reasoning in a structured form instead, use adaptive thinking.
Configures the transformations the server applies to this image before the model observes it. Each key names a condition the server transforms images for; its value selects the transformation applied. Omitted keys keep their default behavior, and an empty object is equivalent to omitting the field.
Configures the transformations the server applies to this image before the model observes it. Each key names a condition the server transforms images for; its value selects the transformation applied. Omitted keys keep their default behavior, and an empty object is equivalent to omitting the field.
What the server does when this image exceeds the model's maximum image size. "downsize" (the default) scales the image down to fit, which changes the dimensions the model observes without telling you. "error" instead rejects the request with a 400 error naming the image's dimensions and the largest dimensions that fit, so you can scale the image deliberately — your image is never silently scaled down.
What the server does when this image exceeds the model's maximum image size. "downsize" (the default) scales the image down to fit, which changes the dimensions the model observes without telling you. "error" instead rejects the request with a 400 error naming the image's dimensions and the largest dimensions that fit, so you can scale the image deliberately — your image is never silently scaled down.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
A schema to specify Claude's output format in responses. See structured outputs
A schema to specify Claude's output format in responses. See structured outputs
Reflects the raw reasoning the model produced, not the (possibly shorter)
summarized thinking text returned in the response body. Computed by
re-tokenizing the raw reasoning text, so it may differ from the model's exact
generation count by a small number of tokens. Always ≤ output_tokens;
output_tokens - thinking_tokens approximates the non-reasoning output.
Pass redacted_thinking blocks back to the API unchanged when continuing a multi-turn conversation.
See extended thinking for details.
This is an opaque field and should not be interpreted or parsed. When passing thinking blocks back to the API (required when using tools with extended thinking), pass them back exactly as received, with this field intact.
See extended thinking for details.
Must be ≥1024 and less than max_tokens.
See extended thinking for details.
When enabled, responses include thinking content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your max_tokens limit.
See extended thinking for details.
Per-frame increment of a coarse, running estimate of the tokens this thinking block has produced so far. Present whenever the thinking-token-count-2026-05-13 beta is set; null unless thinking.display resolves to "omitted" and a count is due this frame. Sum the increments across thinking_delta frames on this block for a progress indicator. Each increment is a non-negative multiple of a fixed quantum and the cadence is rate-limited, so this is a deliberately lossy display hint, not a billable count; usage.output_tokens remains authoritative.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
Create a cache control breakpoint at this content block.
Create a cache control breakpoint at this content block.
This may be one the following values:
5m: 5 minutes1h: 1 hour
Defaults to 5m. See prompt caching pricing for details.
The two letter ISO country code of the user.
The two letter ISO country code of the user.
The IANA timezone of the user.
The IANA timezone of the user.