docs: point the install commands at the 2.0.0a3 release

2.0.0a3 went out today; the book's install commands pinned a2. Every page tells the reader to use the newest alpha, so they now pin a3.

Author: maxisbey

README.v2.md

@@ -19,7 +19,7 @@
 >
 > v2 is a major rework of the SDK, both to support the [2026-07-28 MCP specification release](https://blog.modelcontextprotocol.io/posts/2026-07-28-release-candidate/) and to fix long-standing architectural issues. See the [migration guide](https://py.sdk.modelcontextprotocol.io/v2/migration/) for what's changed. We're targeting a beta on 2026-06-30 and a stable v2 on 2026-07-27, alongside the spec release. Before stable, we plan to add a significant set of backwards compatibility shims so the final upgrade is much smaller than today's diff.
 >
-> **v1.x is the only stable release line and remains recommended for production.** It is in maintenance mode and continues to receive critical bug fixes and security patches. Installers never select a pre-release unless you opt in (for example `pip install mcp==2.0.0a2`), so existing installs are unaffected. **If your package depends on `mcp`, add a `<2` upper bound to your version constraint (for example `mcp>=1.27,<2`) before the stable release lands.**
+> **v1.x is the only stable release line and remains recommended for production.** It is in maintenance mode and continues to receive critical bug fixes and security patches. Installers never select a pre-release unless you opt in (for example `pip install mcp==2.0.0a3`), so existing installs are unaffected. **If your package depends on `mcp`, add a `<2` upper bound to your version constraint (for example `mcp>=1.27,<2`) before the stable release lands.**
 >
 > Try the alpha and tell us what breaks: [#python-sdk-dev on the MCP Contributors Discord](https://discord.gg/6CSzBmMkjX). For v1 documentation, see [the v1.x README](https://github.com/modelcontextprotocol/python-sdk/blob/v1.x/README.md).
 
@@ -44,10 +44,10 @@ Python 3.10+.
 ## Installation
 
 ```bash
-uv add "mcp[cli]==2.0.0a2"          # or: pip install "mcp[cli]==2.0.0a2"
+uv add "mcp[cli]==2.0.0a3"          # or: pip install "mcp[cli]==2.0.0a3"
 ```
 
-The pin matters while v2 is in pre-release: an unpinned install resolves to the latest stable v1.x, which this README does not describe. Check [PyPI](https://pypi.org/project/mcp/#history) for the newest pre-release, and use `uv run --with "mcp==2.0.0a2"` for one-off commands.
+The pin matters while v2 is in pre-release: an unpinned install resolves to the latest stable v1.x, which this README does not describe. Check [PyPI](https://pypi.org/project/mcp/#history) for the newest pre-release, and use `uv run --with "mcp==2.0.0a3"` for one-off commands.
 
 ## A server in 15 lines
 

docs/index.md

@@ -20,13 +20,13 @@ Python 3.10+.
 === "uv"
 
     ```bash
-    uv add "mcp[cli]==2.0.0a2"
+    uv add "mcp[cli]==2.0.0a3"
     ```
 
 === "pip"
 
     ```bash
-    pip install "mcp[cli]==2.0.0a2"
+    pip install "mcp[cli]==2.0.0a3"
     ```
 
 The `[cli]` extra gives you the `mcp` command; you'll want it for development.

docs/installation.md

@@ -7,13 +7,13 @@ These docs describe **v2**, which is in alpha, so the version pin is not optiona
 === "uv"
 
     ```bash
-    uv add "mcp[cli]==2.0.0a2"
+    uv add "mcp[cli]==2.0.0a3"
     ```
 
 === "pip"
 
     ```bash
-    pip install "mcp[cli]==2.0.0a2"
+    pip install "mcp[cli]==2.0.0a3"
     ```
 
 !!! warning "Why the pin"
@@ -22,7 +22,7 @@ These docs describe **v2**, which is in alpha, so the version pin is not optiona
     [release history](https://pypi.org/project/mcp/#history) for the newest alpha before you copy
     the line above.
 
-    The same applies to one-off commands: `uv run --with "mcp==2.0.0a2" ...`, not `uv run --with mcp ...`.
+    The same applies to one-off commands: `uv run --with "mcp==2.0.0a3" ...`, not `uv run --with mcp ...`.
 
     If your *package* depends on `mcp`, add a `<2` upper bound (for example `mcp>=1.27,<2`) before
     the stable v2 lands so the major version bump doesn't surprise you.