What causes "streaming is not supported" in spring-projects/spring-ai?

Implement stream(Prompt) in your ChatModel, e.g. wrapping the blocking call() result: Flux.just(new ChatResponse(List.of(new Generation(...)))) or map the full response to a Flux.

spring-projects/spring-ai · error · UnsupportedOperationException

streaming is not supported

Error message

streaming is not supported

What it means

ChatModel.stream(Prompt) is a default interface method that throws UnsupportedOperationException to signal the model implementation does not support streaming responses. It exists so single-shot models can implement only call() without being forced to provide a streaming API. Calling stream() on such an implementation always fails with this message.

Source

Thrown at spring-ai-model/src/main/java/org/springframework/ai/chat/model/ChatModel.java:65

	/**
	 * Gets the chat options for this model.
	 * @return the chat options
	 * @since 2.0.0
	 */
	default ChatOptions getOptions() {
		return ChatOptions.builder().build();
	}

	/**
	 * @deprecated use {@link #getOptions()} instead.
	 */
	@Deprecated(forRemoval = true)
	default ChatOptions getDefaultOptions() {
		return getOptions();
	}

	default Flux<ChatResponse> stream(Prompt prompt) {
		throw new UnsupportedOperationException("streaming is not supported");
	}

}

View on GitHub (pinned to 98a7beda4f)

Solutions

Implement stream(Prompt) in your ChatModel, e.g. wrapping the blocking call() result: Flux.just(new ChatResponse(List.of(new Generation(...)))) or map the full response to a Flux.
Use the blocking call(Prompt) API instead of streaming if streaming is not needed.
Choose a model/adapters build that supports streaming for the target provider.

Example fix

// before
Flux<ChatResponse> flux = chatModel.stream(new Prompt("hi"));
// after
ChatResponse response = chatModel.call(new Prompt("hi"));

Defensive patterns

Strategy: type-guard

Validate before calling

if (chatModel.getClass().getMethod("stream", Prompt.class).getDeclaringClass() == ChatModel.class) { throw new IllegalStateException("model does not support streaming"); }

Type guard

boolean supportsStreaming(ChatModel m) { try { return m.getClass().getMethod("stream", Prompt.class).getDeclaringClass() != ChatModel.class; } catch (NoSuchMethodException e) { return false; } }

Try / catch

try { return chatModel.stream(prompt); } catch (UnsupportedOperationException e) { return Flux.just(chatModel.call(prompt)); }

Prevention

Check whether your model adapter implements stream() before using ChatClient streaming APIs
Write an integration test that calls stream() on every configured model
Prefer blocking call() when streaming is not required

When it happens

Trigger: Calling ChatClient (flux stream paths) or directly calling stream(prompt) on a ChatModel whose concrete class does not override stream(), e.g. in tests like whenSimplePromptThenFluxChatClientResponse.

Common situations: Developers switch a ChatClient from call() to .stream()/Flux output while the configured model adapter only implements the blocking call() method; occurs after swapping model providers or using custom model wrappers.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of spring-projects/spring-ai@98a7beda4f (2026-09-11). Data as JSON: /api/errors/352f486e6d1a3e92. Report an issue: GitHub.