diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 54dc4e5..ad54505 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,13 +38,14 @@ jobs:
             ${{ runner.os }}-mix-
       - name: Install Mix dependencies
         run: nix develop -c mix deps.get
-      - name: Compile project
-        run: nix develop -c mix compile --warnings-as-errors
+      # Type-check gate: replaces Dialyzer. Elixir 1.20's built-in
+      # set-theoretic type checker runs during `mix compile`; its findings
+      # surface as compile warnings, and --warnings-as-errors fails CI on them.
+      - name: Compile project (type-check gate)
+        run: nix develop -c mix compile --warnings-as-errors --force
       - name: Run tests
         run: nix develop -c mix test
       - name: Check code formatting
         run: nix develop -c mix format --check-formatted
       - name: Run Credo
         run: nix develop -c mix credo
-      - name: Run Dialyzer
-        run: nix develop -c mix dialyzer
diff --git a/DEVELOPMENT.md b/DEVELOPMENT.md
index ba78813..b33ef6f 100644
--- a/DEVELOPMENT.md
+++ b/DEVELOPMENT.md
@@ -52,16 +52,15 @@ Configuration is in `.credo.exs`. Current settings:
 - Strict consistency checks enabled
 - TODOs allowed (warning only)
 
-### Dialyzer
+### Type checking
 
-Static type analysis using Dialyzer:
+Static type analysis is handled by Elixir's built-in set-theoretic
+(gradual) type checker, which runs automatically during `mix compile`.
+Treat its warnings as errors to gate on them:
 
 ```bash
-# Run Dialyzer (first run will be slow while building PLT)
-mix dialyzer
-
-# Clean PLT cache
-rm -rf priv/plts/
+# Type-check the project (forces a full recompile so all warnings surface)
+mix compile --warnings-as-errors --force
 ```
 
 PLT files are cached in `priv/plts/` and excluded from git.
@@ -140,10 +139,9 @@ Tests run on multiple Elixir and OTP versions:
    - Runs Credo in strict mode
    - Uses dependency and build caching
 
-2. **Dialyzer Job**
-   - Runs on latest Elixir/OTP only
-   - Caches PLT files for faster runs
-   - Performs static type analysis
+2. **Type-check gate**
+   - Part of the compile step (`mix compile --warnings-as-errors --force`)
+   - Surfaces the built-in set-theoretic type checker's findings as errors
 
 ## Code Style Guidelines
 
@@ -240,14 +238,11 @@ mix deps.get
 mix test
 ```
 
-### Dialyzer Issues
+### Type-check Issues
 
 ```bash
-# Clean PLT cache
-rm -rf priv/plts/
-
-# Rebuild PLT
-mix dialyzer
+# Force a full recompile so all type-checker warnings surface
+mix compile --warnings-as-errors --force
 ```
 
 ### Formatting Conflicts
@@ -274,5 +269,4 @@ mix format --check-formatted
 
 - **Mix tasks**: `mix help`
 - **Credo**: `mix credo --help`
-- **Dialyzer**: `mix dialyzer --help`
 - **Tests**: `mix help test`
diff --git a/README.md b/README.md
index f15cd85..1548a84 100644
--- a/README.md
+++ b/README.md
@@ -380,8 +380,9 @@ mix credo --strict
 # Generate documentation
 mix docs
 
-# Run Dialyzer (type checking)
-mix dialyzer
+# Type checking (Elixir's built-in set-theoretic type checker runs at compile time;
+# treat its warnings as errors to gate on them)
+mix compile --warnings-as-errors --force
 ```
 
 ### Pre-commit Hook
diff --git a/lib/agent_obs/req_llm.ex b/lib/agent_obs/req_llm.ex
index 27913ce..5bcd67e 100644
--- a/lib/agent_obs/req_llm.ex
+++ b/lib/agent_obs/req_llm.ex
@@ -713,7 +713,6 @@ defmodule AgentObs.ReqLLM do
   - `[:agent_obs, :tool, :exception]` - If tool execution fails
   """
   @spec trace_tool_execution(struct(), map(), keyword()) :: {:ok, term()} | {:error, term()}
-  @dialyzer {:nowarn_function, trace_tool_execution: 3}
   def trace_tool_execution(tool, tool_call, opts \\ []) do
     _ = opts
 
@@ -726,7 +725,7 @@ defmodule AgentObs.ReqLLM do
           {:error, error}
 
         # ReqLLM.Tool.execute can return raw values when the callback doesn't wrap in {:ok, _}
-        # Dialyzer thinks this is unreachable, but it happens in practice (see integration tests)
+        # (the typespec marks this as unreachable, but it happens in practice — see integration tests)
         result ->
           {:ok, result, %{result: result}}
       end
diff --git a/mix.exs b/mix.exs
index 1276154..41ed22d 100644
--- a/mix.exs
+++ b/mix.exs
@@ -14,9 +14,6 @@ defmodule AgentObs.MixProject do
       description: description(),
       package: package(),
       docs: docs(),
-      dialyzer: [
-        plt_file: {:no_warn, "priv/plts/dialyzer.plt"}
-      ],
       aliases: aliases()
     ]
   end
@@ -43,7 +40,6 @@ defmodule AgentObs.MixProject do
 
       # Development and testing dependencies
       {:ex_doc, "~> 0.40", only: :dev, runtime: false},
-      {:dialyxir, "~> 1.4", only: [:dev, :test], runtime: false},
       {:credo, "~> 1.7", only: [:dev, :test], runtime: false}
     ]
   end
diff --git a/mix.lock b/mix.lock
index e2b19c1..70eac9f 100644
--- a/mix.lock
+++ b/mix.lock
@@ -10,10 +10,8 @@
   "crontab": {:hex, :crontab, "1.2.0", "503611820257939d5d0fd272eb2b454f48a470435a809479ddc2c40bb515495c", [:mix], [{:ecto, "~> 1.0 or ~> 2.0 or ~> 3.0", [hex: :ecto, repo: "hexpm", optional: true]}], "hexpm", "ebd7ef4d831e1b20fa4700f0de0284a04cac4347e813337978e25b4cc5cc2207"},
   "ctx": {:hex, :ctx, "0.6.0", "8ff88b70e6400c4df90142e7f130625b82086077a45364a78d208ed3ed53c7fe", [:rebar3], [], "hexpm", "a14ed2d1b67723dbebbe423b28d7615eb0bdcba6ff28f2d1f1b0a7e1d4aa5fc2"},
   "deep_merge": {:hex, :deep_merge, "1.0.0", "b4aa1a0d1acac393bdf38b2291af38cb1d4a52806cf7a4906f718e1feb5ee961", [:mix], [], "hexpm", "ce708e5f094b9cd4e8f2be4f00d2f4250c4095be93f8cd6d018c753894885430"},
-  "dialyxir": {:hex, :dialyxir, "1.4.7", "dda948fcee52962e4b6c5b4b16b2d8fa7d50d8645bbae8b8685c3f9ecb7f5f4d", [:mix], [{:erlex, ">= 0.2.8", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "b34527202e6eb8cee198efec110996c25c5898f43a4094df157f8d28f27d9efe"},
   "dotenvy": {:hex, :dotenvy, "1.1.1", "00e318f3c51de9fafc4b48598447e386f19204dc18ca69886905bb8f8b08b667", [:mix], [], "hexpm", "c8269471b5701e9e56dc86509c1199ded2b33dce088c3471afcfef7839766d8e"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.45", "cba8369ab2a1342e419bc2760eec731b17be828941dcf494045d44766227e1d5", [:mix], [], "hexpm", "d3ec045bf122965db20c0bdb420e19ee1415843135327124918473feb4b328e8"},
-  "erlex": {:hex, :erlex, "0.2.9", "7debbbaa9f4f368b8cd648983e0f1d7963028508e9c59e9d4ed504e94ef52a55", [:mix], [], "hexpm", "8cfffc0ec7159e6d73de2ab28a588064de80f88b2798d5cbe4482cbbc200178b"},
   "ex_aws_auth": {:hex, :ex_aws_auth, "1.4.1", "2f4faf59dd62933c52faf5c026f22b6b9b7d143cf30ee462204a646e3304761f", [:mix], [{:jason, "~> 1.4", [hex: :jason, repo: "hexpm", optional: true]}, {:req, "~> 0.5", [hex: :req, repo: "hexpm", optional: true]}], "hexpm", "42ea14c586689652f51906c797378a07822b65b32febd22067b4e93ff9dc7d4f"},
   "ex_doc": {:hex, :ex_doc, "0.40.3", "4a972ffe64bc07dc605af487e98fc19b72a4185f55ca031b94c0552d6071c1d9", [:mix], [{:earmark_parser, "~> 1.4.44", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_c, ">= 0.1.0", [hex: :makeup_c, repo: "hexpm", optional: true]}, {:makeup_elixir, "~> 0.14 or ~> 1.0", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1 or ~> 1.0", [hex: :makeup_erlang, repo: "hexpm", optional: false]}, {:makeup_html, ">= 0.1.0", [hex: :makeup_html, repo: "hexpm", optional: true]}], "hexpm", "2756e357742fecd9749b489b85d67c9ce99c465f2e75728d9e6dc8d704b973de"},
   "expo": {:hex, :expo, "1.1.1", "4202e1d2ca6e2b3b63e02f69cfe0a404f77702b041d02b58597c00992b601db5", [:mix], [], "hexpm", "5fb308b9cb359ae200b7e23d37c76978673aa1b06e2b3075d814ce12c5811640"},