Anthropic Messages API
Send a structured list of input messages with text and/or image content, and the model will generate the next message in the conversation. The Messages API supports text, images, tool use, extended thinking, streaming, structured outputs, prompt caching, compaction, and the new advisor tool for pairing executor and higher-intelligence advisor models.
Operations 16
Each operation below carries the questions people ask an LLM about it and the instructions they give an agent to run it. Generated by API Evangelist overlay
4 of 16 operations are conformant: apis.io called them with no credentials and the responses matched this contract. Checked 2026-11-12. how this works · status file
Ask an LLM
“How do I send a prompt to Claude and get a reply back?”
“Can I stream the response and set a system prompt, temperature and max tokens?”
Tell an agent
Ask model {model} to reply to {messages} in at most {max_tokens} tokens.
Send {messages} to {model} with system prompt {system}, capped at {max_tokens} tokens, and stream the answer.
Ask an LLM
“How do I run many Claude prompts at once asynchronously?”
“Does a message batch start processing as soon as I submit it?”
Tell an agent
Submit message batch requests {requests}.
Queue these prompts {requests} as one asynchronous message batch.
Ask an LLM
“Which message batches have I submitted in this workspace, newest first?”
“Can I page backward or forward through my batch list by ID?”
Tell an agent
List my {limit} most recent message batches.
Show the message batches created after batch {after_id}.
GET
/v1/messages/batches/{message_batch_id}
Check a message batch's processing status · Retrieve a Message Batch
conformant
#
Ask an LLM
“Is my message batch done processing yet?”
“Where do I find the results URL for a finished batch?”
Tell an agent
Check the status of message batch {message_batch_id}.
Poll batch {message_batch_id} until it finishes processing.
DELETE
/v1/messages/batches/{message_batch_id}
Delete a finished message batch · Delete a Message Batch
#
Ask an LLM
“Can I delete a message batch that's still processing?”
“How do I clean up an old message batch once it's finished?”
Tell an agent destructive · confirm first
Delete finished message batch {message_batch_id}.
Clean up completed batch {message_batch_id} from my workspace.
POST
/v1/messages/batches/{message_batch_id}/cancel
Cancel an in-progress message batch · Cancel a Message Batch
#
Ask an LLM
“How do I stop a message batch before it finishes?”
“What state does a batch go into right after I cancel it?”
Tell an agent destructive · confirm first
Cancel message batch {message_batch_id}.
Stop processing the rest of batch {message_batch_id} now.
POST
/v1/messages/batches/{message_batch_id}/cancel?beta=true
Cancel a message batch via the beta flag · Cancel a Message Batch
#
Ask an LLM
“Can I cancel a running batch through the beta message batches endpoint?”
“Which beta-flag call halts a batch that's still processing?”
Tell an agent destructive · confirm first
Cancel beta message batch {message_batch_id}.
With the beta flag, halt in-flight batch {message_batch_id}.
GET
/v1/messages/batches/{message_batch_id}/results
Download a message batch's results · Retrieve Message Batch results
#
Ask an LLM
“How do I get the responses back from a completed message batch?”
“Are batch results returned in the same order as my requests?”
Tell an agent
Download the results of batch {message_batch_id}.
Stream the .jsonl results file for message batch {message_batch_id}.
GET
/v1/messages/batches/{message_batch_id}/results?beta=true
Download batch results via the beta flag · Retrieve Message Batch results
#
Ask an LLM
“Can I pull a batch's .jsonl results through the beta endpoint?”
“What's the beta-flag way to read every result line of a batch?”
Tell an agent
Get beta results for message batch {message_batch_id}.
With the beta flag, fetch the result lines for batch {message_batch_id}.
GET
/v1/messages/batches/{message_batch_id}?beta=true
Check a batch's status via the beta flag · Retrieve a Message Batch
conformant
#
Ask an LLM
“How do I poll a batch's progress through the beta message batches endpoint?”
“Does the beta batch lookup return the results URL too?”
Tell an agent
Get beta message batch {message_batch_id}.
With the beta flag, check whether batch {message_batch_id} has ended.
DELETE
/v1/messages/batches/{message_batch_id}?beta=true
Delete a message batch via the beta flag · Delete a Message Batch
#
Ask an LLM
“Can I delete a completed batch through the beta endpoint?”
“What's the beta-flag call to remove an old message batch?”
Tell an agent destructive · confirm first
Delete beta message batch {message_batch_id}.
With the beta flag, remove ended batch {message_batch_id}.
POST
/v1/messages/batches?beta=true
Submit a message batch via the beta flag · Create a Message Batch
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Ask an LLM
“Can I create a message batch with beta features using the beta endpoint?”
“Which beta-flag call queues many message requests in one go?”
Tell an agent
Create a beta message batch from {requests}.
With the beta flag, send {requests} for asynchronous processing.
GET
/v1/messages/batches?beta=true
List message batches via the beta flag · List Message Batches
conformant
#
Ask an LLM
“Which batches does the beta message batches listing show for my workspace?”
“Can I page the beta batch list using a before ID?”
Tell an agent
List beta message batches, {limit} per page.
With the beta flag, show batches created before {before_id}.
POST
/v1/messages/count_tokens
Count the tokens in a message before sending · Count tokens in a Message
#
Ask an LLM
“How many tokens will my prompt use before I actually send it to Claude?”
“Does the token count include tools, images and documents?”
Tell an agent
Count the tokens {messages} would use on {model}.
Estimate input tokens for {messages} with system prompt {system} and tools {tools} on {model}.
POST
/v1/messages/count_tokens?beta=true
Count message tokens including MCP servers (beta) · Count tokens in a Message
#
Ask an LLM
“Can I count tokens for a prompt that uses MCP servers or context management?”
“What's the beta-flag token counter for requests with an output format?”
Tell an agent
With the beta flag, count tokens for {messages} on {model} including MCP servers {mcp_servers}.
Tally beta token usage for {messages} on {model} with context management {context_management}.
Ask an LLM
“How do I call Claude with MCP servers connected directly in the request?”
“Can I set fallback models or an output format on a message using the beta endpoint?”
Tell an agent
With the beta flag, have {model} reply to {messages} in up to {max_tokens} tokens using MCP servers {mcp_servers}.
Send beta message {messages} to {model}, max {max_tokens} tokens, falling back to {fallbacks}.
Documentation
Documentation
https://docs.anthropic.com/en/api/messages
Documentation
https://docs.anthropic.com/en/api/messages-streaming
Specifications
OpenAPI
https://artifacts.apis.io/anthropic/openapi/anthropic-messages-api-openapi.yml
AsyncAPI
https://artifacts.apis.io/anthropic/asyncapi/anthropic-asyncapi.yml
Schemas & Data
JSONSchema
https://artifacts.apis.io/anthropic/json-schema/anthropic-message-schema.json
JSONSchema
https://artifacts.apis.io/anthropic/json-schema/anthropic-tool-use-schema.json
Other Resources
JSONLD
https://artifacts.apis.io/anthropic/json-ld/anthropic-context.jsonld
APIsJSON
https://artifacts.apis.io/anthropic/apis.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-batch-cancel-and-confirm-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-batch-create-poll-results-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-count-tokens-then-message-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-create-workspace-and-add-member-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-discover-model-and-message-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-invite-org-member-and-confirm-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-list-batches-and-fetch-latest-results-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-onboard-member-to-workspace-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-provision-and-promote-workspace-member-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-upload-list-and-cleanup-file-workflow.yml
Arazzo
https://artifacts.apis.io/anthropic/arazzo/anthropic-upload-verify-download-file-workflow.yml