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Inference on Baseten is the path from your application to a model running in Baseten’s infrastructure, whether you use Model APIs for hosted models or deploy your own with Truss. You don’t provision GPUs or build your own routing layer: Baseten authenticates each request, matches it to a deployment environment, and runs it on a replica. The sections below follow how you choose an API, how you want the response delivered (synchronous, streaming, or asynchronous), structured outputs and tool calling, and client tuning, and they assume you already have a Baseten account and an API key. To call popular open models without a Truss project first, use the public OpenAI-compatible endpoint at https://inference.baseten.co/v1 with your Baseten API key and the OpenAI SDK pointed at that base URL. The Model APIs documentation lists models, pricing, and feature support. For what happens after the gateway (routing, replicas, queuing, retries, cold starts), see Request lifecycle.

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Inference API

When you deploy your own model, pick an interface that matches your payloads. Engine-Builder-LLM, BIS-LLM, and BEI expose /v1/chat/completions (or /v1/embeddings for BEI) on https://inference.baseten.co/v1 with OpenAI-compatible parameters for structured outputs, tool calling, reasoning, and streaming. Custom Truss code can use /predict for arbitrary JSON when chat or embeddings are not a good fit. Use the Inference API reference for paths, methods, and errors.

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Synchronous inference

Synchronous calls return a full response in one round trip, which fits interactive use (chat, code completion, classification, embeddings) where the client can wait for the answer. See Call your model for predict-style URLs across development, environment, and published deployments.

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Streaming

Streaming sends tokens as they are generated over server-sent events, which suits long generations and UIs where partial output beats a blank wait. See Streaming for client patterns and engine notes.

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Asynchronous inference

Async inference returns a request ID quickly and completes later via webhook or polling, which suits batch work, long documents, or any case where the caller should not hold a connection open for minutes. See Async inference for webhooks, status endpoints, and failures.

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Structured outputs and tool calling

Structured outputs constrain the model to a JSON schema you define; tool calling lets the model invoke your functions and continue the turn. Both align with OpenAI SDK parameters where supported on Model APIs and engine-backed deployments. Read Structured outputs and Function calling for implementation details.

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Client configuration

For sustained load, tune connection reuse, timeouts, and parallelism. The Baseten Performance Client covers common cases; see Performance client and HTTP client configuration for direct HTTP tuning.