What causes "Unsupported content block type: + block" in spring-projects/spring-ai?

Upgrade spring-ai-anthropic to a version that maps server tool-use and code-execution blocks

Unsupported content block type: + block

Error message

Unsupported content block type: + block

What it means

A warning logged while converting Anthropic response content blocks into Spring AI generations when the block type is one the model does not map: container_upload, server_tool_use, bash_code_execution_tool_result, text_editor_code_execution_tool_result, or code_execution_tool_result. The block is skipped silently (no exception); only its content is dropped from the assistant message.

Solutions

Upgrade spring-ai-anthropic to a version that maps server tool-use and code-execution blocks
Disable server-side tools (code execution etc.) in request options if their outputs are not needed
Extract needed data from the raw Anthropic response yourself before/independently of Spring AI conversion
Treat the warning as informational if you only consume text/tool-call content

Example fix

// before
AnthropicChatOptions options = AnthropicChatOptions.builder()
    .withToolChoices(...) // server tools enabled -> code execution blocks
    .build();
// after
// remove server-side tool config or upgrade driver so blocks are mapped
AnthropicChatOptions options = AnthropicChatOptions.builder()
    .withModel("claude-sonnet-4-5")
    .build();

Defensive patterns

Strategy: type-guard

Validate before calling

// before sending, avoid server-side tools you don't handle
if (options.getToolCallbacks().stream().anyMatch(t -> t.getName().startsWith("bash") || t.getName().startsWith("str_replace"))) {
    logger.warn("Server-side tool requested; response may contain unmapped blocks");
}

Type guard

boolean isMappedBlock(ContentBlock block) {
    return block.isText() || block.isToolUse() || block.isThinking() || block.isToolResult();
}

Try / catch

for (Generation g : response.getResults()) {
    AssistantMessage msg = g.getOutput();
    if (!CollectionUtils.isEmpty(msg.getToolCalls())) { ... }
    // treat missing text as expected when server tools are in play
}
// note: this path is a warning, not an exception — no catch needed

Prevention

Do not enable Anthropic code-execution/server tools unless your spring-ai version maps them
Check the changelog of spring-ai-anthropic for new ContentBlock support before upgrading models
If you need server-tool outputs, read the raw response instead of relying on the mapped AssistantMessage
Treat missing text content as normal when server tool blocks are expected

When it happens

Trigger: Calling the chat model (streaming or non-streaming) with server-side tools enabled — Anthropic's code execution, bash code execution, text editor code execution, or web search container uploads — so the response contains these tool-execution block types.

Common situations: Enabling Anthropic's built-in code-execution / server tools via options or beta headers; upgrading to a model that returns new block types while the Spring AI mapper only knows text, thinking, tool_use and tool_result; proxies injecting server tool blocks.

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/833e7aff96aa7976. Report an issue: GitHub.

Appendix: source

Thrown at models/spring-ai-anthropic/src/main/java/org/springframework/ai/anthropic/AnthropicChatModel.java:1054

				thinkingContents.add(AnthropicThinkingContent.redacted(redactedBlock.data()));
				Map<String, Object> redactedProperties = new HashMap<>();
				redactedProperties.put("data", redactedBlock.data());
				generations.add(new Generation(AssistantMessage.builder().properties(redactedProperties).build(),
						generationMetadata));
			}
			else if (block.isWebSearchToolResult()) {
				WebSearchToolResultBlock wsBlock = block.asWebSearchToolResult();
				if (wsBlock.content().isResultBlocks()) {
					for (WebSearchResultBlock r : wsBlock.content().asResultBlocks()) {
						webSearchAccumulator
							.add(new AnthropicWebSearchResult(r.title(), r.url(), r.pageAge().orElse(null)));
					}
				}
			}
			else if (block.isContainerUpload() || block.isServerToolUse() || block.isBashCodeExecutionToolResult()
					|| block.isTextEditorCodeExecutionToolResult() || block.isCodeExecutionToolResult()) {
				if (logger.isWarnEnabled()) {
					logger.warn("Unsupported content block type: " + block);
				}
			}
		}

		generations.add(new Generation(buildAssistantMessage(textContent.toString(), toolCalls, thinkingContents),
				generationMetadata));

		return generations;
	}

	/**
	 * Creates chat response metadata from the Anthropic message.
	 * @param message the Anthropic message
	 * @param usage the usage information
	 * @return the chat response metadata
	 */
	private ChatResponseMetadata from(Message message, Usage usage, List<Citation> citations,
			List<AnthropicWebSearchResult> webSearchResults, RateLimit rateLimit) {

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