BetaContentBlock.TryPickServerToolUse is not returning server side tool calls for webfetch or websearch.

[andyjmorgan]

Version 12.2.0

foreach (var content in response?.Content ?? [])
{
    if (content.TryPickServerToolUse(out var serverToolUseBlock))
    {
        yield return new ModelResponseServerToolUse()
        {
            // not firing
        };
    }

Not working for Beta.Messages.Create or CreateStreaming.

[sd-st]

Hey, thanks for your report! Do you have a minimal reproducible example so I can debug this locally?

[andyjmorgan]

// See https://aka.ms/new-console-template for more information

using System.Text.Json;
using Anthropic.Core;
using Anthropic.Models.Beta.Messages;

var httpClient = new HttpClient();
httpClient.DefaultRequestHeaders.Add("anthropic-beta", "web-fetch-2025-09-10");
var key = "sk-ant-";
var anthropicClientV2 = new Anthropic.AnthropicClient(
    new ClientOptions { ApiKey = key, HttpClient = httpClient, Timeout = httpClient.Timeout, });

var fetchTool = new BetaToolUnion(new BetaWebFetchTool20250910()
{
    MaxUses = 5,
    Citations = new BetaCitationsConfigParam() { Enabled = true, },
});
var searchTool = new BetaToolUnion(new BetaWebSearchTool20250305(){ MaxUses = 5, });

var existingTools = new List<BetaToolUnion>();
existingTools.Add(fetchTool);
existingTools.Add(searchTool);

var request = new MessageCreateParams()
{
    Model = "claude-haiku-4-5-20251001",
    Messages = [new() { Content = "Search latest news from the internet about Anthropic Claude?", Role = Role.User }],
    MaxTokens = 8000,
    Tools = existingTools,
};

await foreach (var item in anthropicClientV2.Beta.Messages.CreateStreaming(request))
{
    try
    {
        string value = string.Empty;
        value = item.Json.GetRawText();
        var isStartMessage = item.TryPickContentBlockStart(out var start);
        bool isServerToolUse = false;
        if (isStartMessage)
        {
            isServerToolUse = start.ContentBlock.TryPickBetaServerToolUse(out var serverToolUse);
        }
    
        Console.WriteLine("Type: {0}, Value: {1}, IsServerToolMessage: {2}", item.Type.GetString(), value, isServerToolUse);
    }
    catch (Exception ex)
    {
        Console.WriteLine("Exception: {0}", ex.Message);
    }
    
}

Output:

Type: message_start, Value: {"type":"message_start","message":{"model":"claude-haiku-4-5-20251001","id":"msg_01RScBCNYmYi2XMRwH4zhKyh","type":"message","role":"assistant","content":[],"stop_reason":null,"stop_sequence":null,"usage":{"input_tokens":3225,"cache_creation_input_tokens":0,"cache_read_input_tokens":0,"cache_creation":{"ephemeral_5m_input_tokens":0,"ephemeral_1h_input_tokens":0},"output_tokens":26,"service_tier":"standard"}}              }, IsServerToolMessage: False
Exception: Data did not match any variant of BetaRawMessageStreamEvent
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":""}   }, IsServerToolMessage: False
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"{\"query\":"} }, IsServerToolMessage: False
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":" \"Anthropi"}       }, IsServerToolMessage: False
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"c Clau"}         }, IsServerToolMessage: False
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"de latest n"}        }, IsServerToolMessage: False
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"ews 2"}       }, IsServerToolMessage: False
Type: content_block_delta, Value: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"026\"}"}               }, IsServerToolMessage: False
Type: content_block_stop, Value: {"type":"content_block_stop","index":0}, IsServerToolMessage: False

Note the exception.

[andyjmorgan]

also note the need to manually do the headers due to beta flag being missing.

[sd-st]

I think you should be using TryPickBetaWebSearchToolResult for web searches and TryPickBetaWebFetchToolResult for web fetches.

[andyjmorgan]

@sd-st that doesn't give me the search term.