Azure OpenAI Assistants API Reaches August 26 Sunset: What Developers Must Migrate

The Azure OpenAI Assistants API sunset date has arrived

Microsoft's documented retirement date for the Azure OpenAI Assistants API is August 26, 2026. This is not a newly announced deprecation: Microsoft had already published the deadline in its Foundry migration guidance. The material change today is that workloads still built on Assistants API semantics have reached the stated sunset date and should be migrated to the generally available Microsoft Foundry Agents service and the Responses API.

Microsoft's current Foundry migration documentation explicitly maps the old Assistants API wire protocol to the Responses API and tells developers to rewrite agent workloads before the August 2026 sunset.

The programming model changes substantially

The migration is not just an endpoint rename. Microsoft maps classic Threads to Conversations, Messages to Items, Runs to Responses, and Assistants or Agents to versioned Agent Versions. The older create_agent() pattern becomes create_version() using a PromptAgentDefinition.

The current stack also moves away from monthly api-version parameters toward stable v1 routes and consolidates previously separate service endpoints into a Foundry project endpoint plus an OpenAI-compatible v1 endpoint. For Python projects, Microsoft's migration prerequisites call for azure-ai-projects 2.x alongside the openai package.

Developers should therefore treat the change as an application-model migration: state storage, execution flow, SDK calls, endpoint construction and agent lifecycle concepts may all need updates.

Responses replace polled Runs

One of the most visible behavioral changes is execution. In the Assistants model, developers commonly created a Run and polled for completion. In the Responses model, responses are synchronous by default, while Conversations store a richer sequence of items including messages, tool calls and outputs.

This can simplify some control flows but also means existing wrappers around thread/run polling should not simply be pointed at a new URL. Tool invocation, state handling, streaming and error behavior should be retested against the current API.

Foundry Agents is the target service

Microsoft directs Assistants API users to the generally available Microsoft Foundry Agents service. The current Foundry experience includes versioned agents and uses the Responses API as the underlying interaction model.

For organizations that built on the older Foundry classic portal, the migration may also involve terminology and resource changes. Microsoft's documentation maps Azure OpenAI plus Hub resources toward the newer Foundry Resource model and notes updated RBAC role names and endpoint structures.

Regional availability can block a direct migration

A critical operational caveat is region support. Microsoft states that the Responses API and Foundry Agent Service are not available in every Azure region. If an existing Foundry resource is in an unsupported region, current agent features will not work there. Microsoft advises checking regional availability and, when necessary, creating a new Foundry resource in a supported region.

That makes migration planning more than a code exercise. Teams may need to account for data residency, network configuration, private endpoints, identity assignments, capacity and deployment changes if they must move resources across regions.

What teams should verify now

Applications that still depend on Assistants, Threads, Runs or the old azure-ai-inference patterns should identify those dependencies immediately. Microsoft separately retired the azure-ai-inference package on May 30, 2026 and points developers to the openai package for current model access.

A production migration should validate conversation persistence, tools, streaming, authentication, RBAC, quotas, region support, monitoring and rollback behavior before traffic is fully shifted. Teams should also confirm that any classic-only features they depended on have an equivalent in the current Foundry service.

The August 26 date is specifically important because it is Microsoft's published Assistants API sunset. It should not be described as a new Microsoft announcement made today, nor should it be generalized into a claim that every older Foundry capability retires on the same date.