diff --git a/Library/Homebrew/api.rb b/Library/Homebrew/api.rb
index 4b208fd0ec..7798262da8 100644
--- a/Library/Homebrew/api.rb
+++ b/Library/Homebrew/api.rb
@@ -21,6 +21,7 @@ module Homebrew
     module_function
 
     API_DOMAIN = "https://formulae.brew.sh/api"
+    HOMEBREW_CACHE_API = (HOMEBREW_CACHE/"api").freeze
 
     sig { params(endpoint: String, json: T::Boolean).returns(T.any(String, Hash)) }
     def fetch(endpoint, json: true)
diff --git a/Library/Homebrew/api/formula.rb b/Library/Homebrew/api/formula.rb
index 5e0774230b..dabdce75d4 100644
--- a/Library/Homebrew/api/formula.rb
+++ b/Library/Homebrew/api/formula.rb
@@ -20,6 +20,17 @@ module Homebrew
         def fetch(name)
           Homebrew::API.fetch "#{formula_api_path}/#{name}.json"
         end
+
+        sig { returns(Array) }
+        def all_formulae
+          @all_formulae ||= begin
+            json_formulae = JSON.parse((HOMEBREW_CACHE_API/"#{formula_api_path}.json").read)
+
+            json_formulae.to_h do |json_formula|
+              [json_formula["name"], json_formula.except("name")]
+            end
+          end
+        end
       end
     end
   end
diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 429d7e5c5f..1a1ce32233 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -764,7 +764,7 @@ then
   export HOMEBREW_DEVELOPER_MODE="1"
 fi
 
-if [[ -n "${HOMEBREW_INSTALL_FROM_API}" && -n "${HOMEBREW_DEVELOPER_COMMAND}" ]]
+if [[ -n "${HOMEBREW_INSTALL_FROM_API}" && -n "${HOMEBREW_DEVELOPER_COMMAND}" && "${HOMEBREW_COMMAND}" != "irb" ]]
 then
   odie "Developer commands cannot be run while HOMEBREW_INSTALL_FROM_API is set!"
 elif [[ -n "${HOMEBREW_INSTALL_FROM_API}" && -n "${HOMEBREW_DEVELOPER_MODE}" ]]
diff --git a/Library/Homebrew/cli/named_args.rb b/Library/Homebrew/cli/named_args.rb
index 9d484a141d..cd2a9ab899 100644
--- a/Library/Homebrew/cli/named_args.rb
+++ b/Library/Homebrew/cli/named_args.rb
@@ -94,11 +94,6 @@ module Homebrew
         unreadable_error = nil
 
         if only != :cask
-          if prefer_loading_from_api && Homebrew::EnvConfig.install_from_api? &&
-             Homebrew::API::Bottle.available?(name)
-            Homebrew::API::Bottle.fetch_bottles(name)
-          end
-
           begin
             formula = case method
             when nil, :factory
diff --git a/Library/Homebrew/cmd/info.rb b/Library/Homebrew/cmd/info.rb
index a541b36ef1..a9e489bc4f 100644
--- a/Library/Homebrew/cmd/info.rb
+++ b/Library/Homebrew/cmd/info.rb
@@ -252,16 +252,7 @@ module Homebrew
   def info_formula(f, args:)
     specs = []
 
-    if Homebrew::EnvConfig.install_from_api? && Homebrew::API::Bottle.available?(f.name)
-      info = Homebrew::API::Bottle.fetch(f.name)
-
-      latest_version = info["pkg_version"].split("_").first
-      bottle_exists = info["bottles"].key?(Utils::Bottles.tag.to_s) || info["bottles"].key?("all")
-
-      s = "stable #{latest_version}"
-      s += " (bottled)" if bottle_exists
-      specs << s
-    elsif (stable = f.stable)
+    if (stable = f.stable)
       s = "stable #{stable.version}"
       s += " (bottled)" if stable.bottled? && f.pour_bottle?
       specs << s
diff --git a/Library/Homebrew/cmd/update.sh b/Library/Homebrew/cmd/update.sh
index 551a063257..706fb936dd 100644
--- a/Library/Homebrew/cmd/update.sh
+++ b/Library/Homebrew/cmd/update.sh
@@ -745,6 +745,20 @@ EOS
     fi
   done
 
+  if [[ -n "${HOMEBREW_INSTALL_FROM_API}" ]]
+  then
+    mkdir -p "${HOMEBREW_CACHE}/api"
+    # TODO: etags?
+    curl \
+      "${CURL_DISABLE_CURLRC_ARGS[@]}" \
+      --fail --compressed --silent --max-time 5 \
+      --location --output "${HOMEBREW_CACHE}/api/formula.json" \
+      --user-agent "${HOMEBREW_USER_AGENT_CURL}" \
+      "https://formulae.brew.sh/api/formula.json"
+    # TODO: we probably want to print an error if this fails.
+    # TODO: set HOMEBREW_UPDATED or HOMEBREW_UPDATE_FAILED
+  fi
+
   safe_cd "${HOMEBREW_REPOSITORY}"
 
   # HOMEBREW_UPDATE_AUTO wasn't modified in subshell.
diff --git a/Library/Homebrew/cmd/upgrade.rb b/Library/Homebrew/cmd/upgrade.rb
index b7fa29b427..5b5ef6b607 100644
--- a/Library/Homebrew/cmd/upgrade.rb
+++ b/Library/Homebrew/cmd/upgrade.rb
@@ -161,19 +161,6 @@ module Homebrew
       puts pinned.map { |f| "#{f.full_specified_name} #{f.pkg_version}" } * ", "
     end
 
-    if Homebrew::EnvConfig.install_from_api?
-      formulae_to_install.map! do |formula|
-        next formula if formula.head?
-        next formula if formula.tap.present? && !formula.core_formula?
-        next formula unless Homebrew::API::Bottle.available?(formula.name)
-
-        Homebrew::API::Bottle.fetch_bottles(formula.name)
-        Formulary.factory(formula.name)
-      rescue FormulaUnavailableError
-        formula
-      end
-    end
-
     if formulae_to_install.empty?
       oh1 "No packages to upgrade"
     else
diff --git a/Library/Homebrew/formulary.rb b/Library/Homebrew/formulary.rb
index 4889b5785e..fa20e35d9c 100644
--- a/Library/Homebrew/formulary.rb
+++ b/Library/Homebrew/formulary.rb
@@ -6,6 +6,8 @@ require "extend/cachable"
 require "tab"
 require "utils/bottles"
 
+require "active_support/core_ext/hash/deep_transform_values"
+
 # The {Formulary} is responsible for creating instances of {Formula}.
 # It is not meant to be used directly from formulae.
 #
@@ -44,6 +46,8 @@ module Formulary
       remove_const(namespace.demodulize)
     end
 
+    remove_const("FormulaNamespaceAPI")
+
     super
   end
 
@@ -392,6 +396,102 @@ module Formulary
     end
   end
 
+  # Load formulae from the API.
+  class FormulaAPILoader < FormulaLoader
+    def initialize(name)
+      super name, Formulary.core_path(name)
+    end
+
+    def klass(flags:, ignore_errors:)
+      namespace = "FormulaNamespaceAPI"
+      mod = if Formulary.const_defined?(namespace)
+        Formulary.const_get(namespace)
+      else
+        Formulary.const_set(namespace, Module.new)
+      end
+
+      mod.send(:remove_const, :BUILD_FLAGS) if mod.const_defined?(:BUILD_FLAGS)
+      mod.const_set(:BUILD_FLAGS, flags)
+
+      class_s = Formulary.class_s(name)
+      if mod.const_defined?(class_s)
+        mod.const_get(class_s)
+      else
+        json_formula = Homebrew::API::Formula.all_formulae[name]
+        klass = Class.new(::Formula) do
+          desc json_formula["desc"]
+          homepage json_formula["homepage"]
+          license json_formula["license"]
+          revision json_formula["revision"]
+          version_scheme json_formula["version_scheme"]
+
+          if (urls_stable = json_formula["urls"]["stable"]).present?
+            stable do
+              url urls_stable["url"]
+              version json_formula["versions"]["stable"]
+            end
+          end
+
+          if (bottles_stable = json_formula["bottle"]["stable"]).present?
+            bottle do
+              root_url bottles_stable["root_url"]
+              bottles_stable["files"].each do |tag, bottle_spec|
+                cellar = bottle_spec["cellar"]
+                cellar = cellar[1..].to_sym if cellar.start_with?(":")
+                sha256 cellar: cellar, tag.to_sym => bottle_spec["sha256"]
+              end
+            end
+          end
+
+          if (keg_only_reason = json_formula["keg_only_reason"]).present?
+            reason = keg_only_reason["reason"]
+            reason = reason[1..].to_sym if reason.start_with?(":")
+            keg_only reason, keg_only_reason["explanation"]
+          end
+
+          if (deprecation_date = json_formula["deprecation_date"]).present?
+            deprecate! date: deprecation_date, because: json_formula["deprecation_reason"]
+          end
+
+          if (disable_date = json_formula["disable_date"]).present?
+            disable! date: disable_date, because: json_formula["disable_reason"]
+          end
+
+          json_formula["build_dependencies"].each do |dep|
+            depends_on dep => :build
+          end
+
+          json_formula["dependencies"].each do |dep|
+            depends_on dep
+          end
+
+          json_formula["recommended_dependencies"].each do |dep|
+            depends_on dep => :recommended
+          end
+
+          json_formula["optional_dependencies"].each do |dep|
+            depends_on dep => :optional
+          end
+
+          json_formula["uses_from_macos"].each do |dep|
+            dep = dep.deep_transform_values(&:to_sym) if dep.is_a?(Hash)
+            uses_from_macos dep
+          end
+
+          def install
+            raise "Cannot build from source from abstract formula."
+          end
+
+          @caveats_string = json_formula["caveats"]
+          def caveats
+            @caveats_string
+          end
+        end
+        mod.const_set(class_s, klass)
+      end
+    end
+  end
+
   # Return a {Formula} instance for the given reference.
   # `ref` is a string containing:
   #
@@ -539,11 +639,9 @@ module Formulary
     when URL_START_REGEX
       return FromUrlLoader.new(ref)
     when HOMEBREW_TAP_FORMULA_REGEX
-      # If `homebrew/core` is specified and not installed, check whether the formula is already installed.
       if ref.start_with?("homebrew/core/") && !CoreTap.instance.installed? && Homebrew::EnvConfig.install_from_api?
         name = ref.split("/", 3).last
-        possible_keg_formula = Pathname.new("#{HOMEBREW_PREFIX}/opt/#{name}/.brew/#{name}.rb")
-        return FormulaLoader.new(name, possible_keg_formula) if possible_keg_formula.file?
+        return FormulaAPILoader.new(name) if Homebrew::API::Formula.all_formulae.key?(name)
       end
 
       return TapLoader.new(ref, from: from)
@@ -557,6 +655,12 @@ module Formulary
     possible_alias = CoreTap.instance.alias_dir/ref
     return AliasLoader.new(possible_alias) if possible_alias.file?
 
+    if !CoreTap.instance.installed? &&
+       Homebrew::EnvConfig.install_from_api? &&
+       Homebrew::API::Formula.all_formulae.key?(ref)
+      return FormulaAPILoader.new(ref)
+    end
+
     possible_tap_formulae = tap_paths(ref)
     raise TapFormulaAmbiguityError.new(ref, possible_tap_formulae) if possible_tap_formulae.size > 1
 
diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index 173c13ce40..7a2fba9256 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -142,8 +142,6 @@ class Tap
   # The remote repository name of this {Tap}.
   # e.g. `user/homebrew-repo`
   def remote_repo
-    raise TapUnavailableError, name unless installed?
-
     return unless remote
 
     @remote_repo ||= remote.delete_prefix("https://github.com/")
@@ -795,6 +793,12 @@ class CoreTap < Tap
     safe_system HOMEBREW_BREW_FILE, "tap", instance.name
   end
 
+  def remote
+    super if installed? || !Homebrew::EnvConfig.install_from_api?
+
+    Homebrew::EnvConfig.core_git_remote
+  end
+
   # CoreTap never allows shallow clones (on request from GitHub).
   def install(quiet: false, clone_target: nil, force_auto_update: nil, custom_remote: false)
     remote = Homebrew::EnvConfig.core_git_remote # set by HOMEBREW_CORE_GIT_REMOTE