diff --git a/Library/Homebrew/api.rb b/Library/Homebrew/api.rb
index a6dadf6fa6c3f..49bb507b1df49 100644
--- a/Library/Homebrew/api.rb
+++ b/Library/Homebrew/api.rb
@@ -3,7 +3,6 @@
 
 require "api/analytics"
 require "api/cask"
-require "api/cask-source"
 require "api/formula"
 require "api/versions"
 require "extend/cachable"
@@ -23,23 +22,20 @@ module API
     HOMEBREW_CACHE_API = (HOMEBREW_CACHE/"api").freeze
     MAX_RETRIES = 3
 
-    sig { params(endpoint: String, json: T::Boolean).returns(T.any(String, Hash)) }
-    def fetch(endpoint, json: true)
+    sig { params(endpoint: String).returns(Hash) }
+    def fetch(endpoint)
       return cache[endpoint] if cache.present? && cache.key?(endpoint)
 
       api_url = "#{API_DOMAIN}/#{endpoint}"
       output = Utils::Curl.curl_output("--fail", api_url, max_time: 5)
       raise ArgumentError, "No file found at #{Tty.underline}#{api_url}#{Tty.reset}" unless output.success?
 
-      cache[endpoint] = if json
-        JSON.parse(output.stdout)
-      else
-        output.stdout
-      end
+      cache[endpoint] = JSON.parse(output.stdout)
     rescue JSON::ParserError
       raise ArgumentError, "Invalid JSON file: #{Tty.underline}#{api_url}#{Tty.reset}"
     end
 
+    sig { params(endpoint: String, target: Pathname).returns(Hash) }
     def fetch_json_api_file(endpoint, target:)
       retry_count = 0
 
@@ -58,5 +54,19 @@ def fetch_json_api_file(endpoint, target:)
         retry
       end
     end
+
+    sig { params(filepath: String, repo: String, git_head: T.nilable(String)).returns(String) }
+    def fetch_file_source(filepath, repo:, git_head: nil)
+      git_head ||= "master"
+      endpoint = "#{git_head}/#{filepath}"
+      return cache[endpoint] if cache.present? && cache.key?(endpoint)
+
+      raw_url = "https://raw.githubusercontent.com/#{repo}/#{endpoint}"
+      puts "Fetching #{raw_url}..."
+      output = Utils::Curl.curl_output("--fail", raw_url, max_time: 5)
+      raise ArgumentError, "No file found at #{Tty.underline}#{raw_url}#{Tty.reset}" unless output.success?
+
+      cache[endpoint] = output.stdout
+    end
   end
 end
diff --git a/Library/Homebrew/api/cask-source.rb b/Library/Homebrew/api/cask-source.rb
deleted file mode 100644
index 0c1cd67a21849..0000000000000
--- a/Library/Homebrew/api/cask-source.rb
+++ /dev/null
@@ -1,29 +0,0 @@
-# typed: false
-# frozen_string_literal: true
-
-module Homebrew
-  module API
-    # Helper functions for using the cask source API.
-    #
-    # @api private
-    module CaskSource
-      class << self
-        extend T::Sig
-
-        sig { params(token: String).returns(Hash) }
-        def fetch(token)
-          token = token.sub(%r{^homebrew/cask/}, "")
-          Homebrew::API.fetch "cask-source/#{token}.rb", json: false
-        end
-
-        sig { params(token: String).returns(T::Boolean) }
-        def available?(token)
-          fetch token
-          true
-        rescue ArgumentError
-          false
-        end
-      end
-    end
-  end
-end
diff --git a/Library/Homebrew/api/cask.rb b/Library/Homebrew/api/cask.rb
index f0ed248cdf809..4f7c4b8e36089 100644
--- a/Library/Homebrew/api/cask.rb
+++ b/Library/Homebrew/api/cask.rb
@@ -10,9 +10,14 @@ module Cask
       class << self
         extend T::Sig
 
-        sig { params(name: String).returns(Hash) }
-        def fetch(name)
-          Homebrew::API.fetch "cask/#{name}.json"
+        sig { params(token: String).returns(Hash) }
+        def fetch(token)
+          Homebrew::API.fetch "cask/#{token}.json"
+        end
+
+        sig { params(token: String, git_head: T.nilable(String)).returns(String) }
+        def fetch_source(token, git_head: nil)
+          Homebrew::API.fetch_file_source "Casks/#{token}.rb", repo: "Homebrew/homebrew-cask", git_head: git_head
         end
 
         sig { returns(Hash) }
diff --git a/Library/Homebrew/cask/cask.rb b/Library/Homebrew/cask/cask.rb
index fa99aa836f50e..02703f440b366 100644
--- a/Library/Homebrew/cask/cask.rb
+++ b/Library/Homebrew/cask/cask.rb
@@ -246,6 +246,7 @@ def to_h
         "conflicts_with" => conflicts_with,
         "container"      => container&.pairs,
         "auto_updates"   => auto_updates,
+        "tap_git_head"   => tap&.git_head,
         "languages"      => languages,
       }
     end
diff --git a/Library/Homebrew/cask/cask_loader.rb b/Library/Homebrew/cask/cask_loader.rb
index 6e66b043ee7fb..79f494a3bc8b4 100644
--- a/Library/Homebrew/cask/cask_loader.rb
+++ b/Library/Homebrew/cask/cask_loader.rb
@@ -212,9 +212,9 @@ def load(config:)
 
         json_cask.deep_symbolize_keys!
 
-        # Use the cask-source API if there are any `*flight` blocks
+        # Download and use the cask source file if there are any `*flight` blocks
         if json_cask[:artifacts].any? { |artifact| FLIGHT_STANZAS.include?(artifact.keys.first) }
-          cask_source = Homebrew::API::CaskSource.fetch(token)
+          cask_source = Homebrew::API::Cask.fetch_source(token, git_head: json_cask[:tap_git_head])
           return FromContentLoader.new(cask_source).load(config: config)
         end
 
@@ -222,7 +222,9 @@ def load(config:)
         json_cask[:artifacts] = json_cask[:artifacts].map(&method(:from_h_hash_gsubs))
         json_cask[:caveats] = from_h_string_gsubs(json_cask[:caveats])
 
-        Cask.new(token, source: cask_source, config: config) do
+        tap = Tap.fetch(json_cask[:tap]) if json_cask[:tap].to_s.include?("/")
+
+        Cask.new(token, tap: tap, source: cask_source, config: config) do
           version json_cask[:version]
 
           if json_cask[:sha256] == "no_check"
@@ -370,7 +372,7 @@ def self.for(ref, need_path: false)
         return loader_class.new(ref)
       end
 
-      if Homebrew::EnvConfig.install_from_api? && !need_path && Homebrew::API::CaskSource.available?(ref)
+      if Homebrew::EnvConfig.install_from_api? && !need_path && Homebrew::API::Cask.all_casks.key?(ref)
         return FromAPILoader.new(ref)
       end
 
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index bb8a0e6bfdf86..aaf6edb60f1f2 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -2126,6 +2126,7 @@ def to_hash
       "disabled"                 => disabled?,
       "disable_date"             => disable_date,
       "disable_reason"           => disable_reason,
+      "tap_git_head"             => tap&.git_head,
     }
 
     if stable
diff --git a/Library/Homebrew/system_config.rb b/Library/Homebrew/system_config.rb
index a019aa4de0333..9f1d969ca5bd2 100644
--- a/Library/Homebrew/system_config.rb
+++ b/Library/Homebrew/system_config.rb
@@ -141,11 +141,15 @@ def describe_curl
 
     def core_tap_config(f = $stdout)
       if CoreTap.instance.installed?
-        f.puts "Core tap ORIGIN: #{core_tap_origin}"
+        f.puts "Core tap origin: #{core_tap_origin}"
         f.puts "Core tap HEAD: #{core_tap_head}"
         f.puts "Core tap last commit: #{core_tap_last_commit}"
         f.puts "Core tap branch: #{core_tap_branch}"
-      else
+      end
+
+      if (formula_json = Homebrew::API::HOMEBREW_CACHE_API/"formula.json") && formula_json.exist?
+        f.puts "Core tap JSON: #{formula_json.mtime.to_s(:short)}"
+      elsif !CoreTap.instance.installed?
         f.puts "Core tap: N/A"
       end
     end
diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index a6aed47cbd432..5c3433cbd8668 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -178,7 +178,7 @@ def git_branch
   def git_head
     raise TapUnavailableError, name unless installed?
 
-    path.git_head
+    @git_head ||= path.git_head
   end
 
   # Time since last git commit for this {Tap}.
diff --git a/Library/Homebrew/test/api/cask_spec.rb b/Library/Homebrew/test/api/cask_spec.rb
index 35c561b8f9c18..b5dd7ec1f2296 100644
--- a/Library/Homebrew/test/api/cask_spec.rb
+++ b/Library/Homebrew/test/api/cask_spec.rb
@@ -41,4 +41,14 @@ def mock_curl_download(stdout:)
       expect(casks_output).to eq casks_hash
     end
   end
+
+  describe "::fetch_source" do
+    it "fetches the source of a cask (defaulting to master when no `git_head` is passed)" do
+      curl_output = OpenStruct.new(stdout: "foo", success?: true)
+      expect(Utils::Curl).to receive(:curl_output)
+        .with("--fail", "https://raw.githubusercontent.com/Homebrew/homebrew-cask/master/Casks/foo.rb", max_time: 5)
+        .and_return(curl_output)
+      described_class.fetch_source("foo", git_head: nil)
+    end
+  end
 end
diff --git a/Library/Homebrew/test/api_spec.rb b/Library/Homebrew/test/api_spec.rb
index ff695bfe7797f..6d639e5c0f96b 100644
--- a/Library/Homebrew/test/api_spec.rb
+++ b/Library/Homebrew/test/api_spec.rb
@@ -21,12 +21,6 @@ def mock_curl_download(stdout:)
   end
 
   describe "::fetch" do
-    it "fetches a text file" do
-      mock_curl_output stdout: text
-      fetched_text = described_class.fetch("foo.txt", json: false)
-      expect(fetched_text).to eq text
-    end
-
     it "fetches a JSON file" do
       mock_curl_output stdout: json
       fetched_json = described_class.fetch("foo.json")
@@ -70,4 +64,19 @@ def mock_curl_download(stdout:)
       }.to raise_error(SystemExit)
     end
   end
+
+  describe "::fetch_file_source" do
+    it "fetches a file" do
+      mock_curl_output stdout: json
+      fetched_json = described_class.fetch_file_source("foo.json", repo: "Homebrew/homebrew-core", git_head: "master")
+      expect(fetched_json).to eq json
+    end
+
+    it "raises an error if the file does not exist" do
+      mock_curl_output success: false
+      expect {
+        described_class.fetch_file_source("bar.txt", repo: "Homebrew/homebrew-core", git_head: "master")
+      }.to raise_error(ArgumentError, /No file found/)
+    end
+  end
 end
diff --git a/Library/Homebrew/test/cask/cmd/list_spec.rb b/Library/Homebrew/test/cask/cmd/list_spec.rb
index 8d397e19f4314..3c1518cafc4f6 100644
--- a/Library/Homebrew/test/cask/cmd/list_spec.rb
+++ b/Library/Homebrew/test/cask/cmd/list_spec.rb
@@ -128,6 +128,7 @@
             "conflicts_with": null,
             "container": null,
             "auto_updates": null,
+            "tap_git_head": null,
             "languages": [
 
             ]
@@ -162,6 +163,7 @@
             "conflicts_with": null,
             "container": null,
             "auto_updates": null,
+            "tap_git_head": null,
             "languages": [
 
             ]
@@ -199,6 +201,7 @@
             "conflicts_with": null,
             "container": null,
             "auto_updates": null,
+            "tap_git_head": null,
             "languages": [
 
             ]
@@ -233,6 +236,7 @@
             "conflicts_with": null,
             "container": null,
             "auto_updates": null,
+            "tap_git_head": null,
             "languages": [
 
             ]
@@ -267,6 +271,7 @@
             "conflicts_with": null,
             "container": null,
             "auto_updates": null,
+            "tap_git_head": null,
             "languages": [
               "zh",
               "en-US"