Letta Conversations API is one of 41 APIs that Letta publishes on the APIs.io network, described by a machine-readable OpenAPI specification.
This API exposes 14 JSON Schema definitions.
Tagged areas include Conversations. The published artifact set on APIs.io includes an OpenAPI specification, API documentation, pricing, a changelog, and 14 JSON Schemas.
This API exposes
13 operations
across 9 paths,
and defines 82 schemas.
It is described by OpenAPI 3.2.0, at version 1.0.0.
Requests are made against 3 base URLs: https://api.letta.com, https://app.letta.com, http://localhost:8283.
The identity and technical contract details declared by the specification.
ToolReturnContent
object
4 properties
3 required
ZAIModelSettings
object
Z.ai (ZhipuAI) model configuration (OpenAI-compatible).
6 properties
OpenAIReasoning
object
1 property
GoogleAIModelSettings
object
6 properties
OpenRouterModelSettings
object
OpenRouter model configuration (OpenAI-compatible).
5 properties
ImageContent
object
2 properties
1 required
ToolCall
object
3 properties
3 required
ClientToolSchema
object
Schema for a client-side tool passed in the request. Client-side tools are executed by the client, not the server. When the agent calls a client-side tool, exe…
3 properties
1 required
BasetenModelSettings
object
Baseten model configuration (OpenAI-compatible).
4 properties
ConversationMessageRequest
object
Request for sending messages to a conversation. Streams by default.
21 properties
XAIModelSettings
object
xAI model configuration (OpenAI-compatible).
5 properties
RedactedReasoningContent
object
Sent via the Anthropic Messages API
2 properties
1 required
MessageCreate
object
Request to create a message
8 properties
2 required
RetrieveStreamRequest
object
7 properties
GeminiThinkingConfig
object
2 properties
Conversation
object
Represents a conversation on an agent for concurrent messaging.
12 properties
2 required
ClientSkillSchema
object
Schema for a client-side skill passed in the request. Client-side skills represent environment-provided capabilities (e.g. project-scoped skills) that are not…
3 properties
3 required
JsonObjectResponseFormat
object
Response format for JSON object responses.
1 property
ReasoningMessage
object
Representation of an agent's internal reasoning. Args: id (str): The ID of the message date (datetime): The date the message was created in ISO format name (Op…
13 properties
3 required
ToolReturnCreate
object
Submit tool return(s) from client-side tool execution. This is the preferred way to send tool results back to the agent after client-side tool execution. It is…
4 properties
1 required
AnthropicModelSettings
object
9 properties
ToolReturnMessage
object
A message representing the return value of a tool call (generated by Letta executing the requested tool). Args: id (str): The ID of the message date (datetime)…
16 properties
5 required
SummarizedReasoningContent
object
The style of reasoning content returned by the OpenAI Responses API
4 properties
2 required
letta__schemas__openai__chat_completion_response__ChatCompletionTokenLogprob
object
4 properties
3 required
LettaUserMessageContentUnion
BedrockModelSettings
object
AWS Bedrock model configuration.
5 properties
CompactionStats
object
Statistics about a memory compaction operation.
6 properties
4 required
ReasoningContent
object
Sent via the Anthropic Messages API
4 properties
2 required
UpdateConversation
object
Request model for updating a conversation.
4 properties
ToolCallContent
object
5 properties
3 required
LettaStopReason
object
The stop reason from Letta indicating why agent loop stopped execution.
2 properties
1 required
GroqModelSettings
object
Groq model configuration (OpenAI-compatible).
5 properties
CompactionResponse
object
3 properties
3 required
ApprovalCreate
object
Input to approve or deny a tool call request
7 properties
letta__schemas__openai__chat_completion_response__ChoiceLogprobs
object
2 properties
LettaToolReturnContentUnion
OpenAIModelSettings
object
7 properties
AzureModelSettings
object
Azure OpenAI model configuration (OpenAI-compatible).
5 properties
TurnTokenData
object
Token data for a single LLM generation turn in a multi-turn agent interaction. Used for RL training to track token IDs and logprobs across all LLM calls, not j…
5 properties
1 required
LettaErrorMessage
object
Error messages are used to notify the client of an error that occurred during the agent's execution.
6 properties
4 required
UserMessage
object
A message sent by the user. Never streamed back on a response, only used for cursor pagination. Args: id (str): The ID of the message date (datetime): The date…
11 properties
3 required
ValidationError
object
3 properties
3 required
SystemMessage
object
A message generated by the system. Never streamed back on a response, only used for cursor pagination. Args: id (str): The ID of the message date (datetime): T…
11 properties
3 required
UrlImage
object
2 properties
1 required
ApprovalRequestMessage
object
A message representing a request for approval to call a tool (generated by the LLM to trigger tool execution). Args: id (str): The ID of the message date (date…
12 properties
3 required
Base64Image
object
4 properties
2 required
letta__schemas__letta_message__ToolReturn
object
6 properties
3 required
EventMessage
object
A message for notifying the developer that an event that has occured (e.g. a compaction). Events are NOT part of the context window.
12 properties
4 required
letta__server__rest_api__routers__v1__conversations__CompactionRequest
object
2 properties
HiddenReasoningMessage
object
Representation of an agent's internal reasoning where reasoning content has been hidden from the response. Args: id (str): The ID of the message date (datetime…
12 properties
3 required
TextResponseFormat
object
Response format for plain text responses.
1 property
TogetherModelSettings
object
Together AI model configuration (OpenAI-compatible).
5 properties
CompactionSettings-Input
object
Configuration for conversation compaction / summarization. Per-model settings (temperature, max tokens, etc.) are derived from the default configuration for th…
7 properties
ToolCallMessage
object
A message representing a request to call a tool (generated by the LLM to trigger tool execution). Args: id (str): The ID of the message date (datetime): The da…
12 properties
3 required
SummaryMessage
object
A message representing a summary of the conversation. Sent to the LLM as a user or system message depending on the provider.
12 properties
3 required
LettaResponse
object
Response object from an agent interaction, consisting of the new messages generated by the agent and usage statistics. The type of the returned messages can be…
5 properties
3 required
ChatGPTOAuthReasoning
object
Reasoning configuration for ChatGPT OAuth models (GPT-5.x, o-series).
1 property
TextContent
object
3 properties
1 required
SummarizedReasoningContentPart
object
2 properties
2 required
GoogleVertexModelSettings
object
6 properties
HTTPValidationError
object
1 property
ApprovalReturn
object
4 properties
2 required
AssistantMessage
object
A message sent by the LLM in response to user input. Used in the LLM context. Args: id (str): The ID of the message date (datetime): The date the message was c…
11 properties
3 required
AnthropicThinking
object
2 properties
SGLangModelSettings
object
SGLang model configuration (OpenAI-compatible runtime with SGLang-specific parsing).
8 properties
LettaPing
object
A ping message used as a keepalive to prevent SSE streams from timing out during long running requests. Args: id (str): The ID of the message date (datetime):…
10 properties
2 required
JsonSchemaResponseFormat
object
Response format for JSON schema-based responses.
2 properties
1 required
ToolCallDelta
object
3 properties
ChatGPTOAuthModelSettings
object
ChatGPT OAuth model configuration (uses ChatGPT backend API).
5 properties
LettaAssistantMessageContentUnion
LettaImage
object
5 properties
1 required
DeepseekModelSettings
object
Deepseek model configuration (OpenAI-compatible).
5 properties
letta__schemas__openai__chat_completion_response__TopLogprob
object
3 properties
2 required
LettaUsageStatistics
object
Usage statistics for the agent interaction. Attributes: completiontokens (int): The number of tokens generated by the agent. prompttokens (int): The number of…
10 properties
ZAIThinking
object
Thinking configuration for ZAI GLM-4.5+ models.
2 properties
CreateConversation
object
Request model for creating a new conversation.
4 properties
OmittedReasoningContent
object
A placeholder for reasoning content we know is present, but isn't returned by the provider (e.g. OpenAI GPT-5 on ChatCompletions)
2 properties
ApprovalResponseMessage
object
A message representing a response form the user indicating whether a tool has been approved to run. Args: id (str): The ID of the message date (datetime): The…
14 properties
2 required
The full machine-readable OpenAPI contract behind this narrative.
Other APIs Letta publishes across the network.
