[See How to Implement.txt below] This Gist shows how to implement a Client model observer for Laravel Passport so that you don't have to be stuck with that weird autoincrementing Client ID.

app\Observers\ClientObserver.php

<?php

namespace App\Observers;

use Laravel\Passport\Client;

class ClientObserver
{
	/**
	 * Listen to the Client creating event.
	 *
	 * @param  \Laravel\Passport\Client  $client
	 * @return void
	 */
	public function creating(Client $client)
	{
		// Set the model ID.
		$client->setAttribute('id', Randomizer::createNumericId()); // This is where you will need to update this code to create the type of random, numeric ID you want.
	}
}

app\Providers\AppServiceProvider.php

<?php

namespace App\Providers;

use Illuminate\Support\ServiceProvider;
use Laravel\Passport\Client;
use Laravel\Passport\Passport;
use App\Observers\ClientObserver;

class AppServiceProvider extends ServiceProvider
{
	/**
	 * Bootstrap any application services.
	 *
	 * @return void
	 */
	public function boot()
	{
		// Register model observers.
		Client::observe(ClientObserver::class);
	}

	/**
	 * Register any application services.
	 *
	 * @return void
	 */
	public function register()
	{
		Passport::ignoreMigrations();
	}
}

database\migrations\2017_01_14_000001_create_oauth_clients_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateOauthClientsTable extends Migration
{
	/**
	 * Run the migrations.
	 *
	 * @return void
	 */
	public function up()
	{
		Schema::create('oauth_clients', function (Blueprint $table) {
			$table->bigInteger('id')->unsigned();
			$table->integer('user_id')->index()->nullable();
			$table->string('name');
			$table->string('secret', 100);
			$table->text('redirect');
			$table->boolean('personal_access_client');
			$table->boolean('password_client');
			$table->boolean('revoked');
			$table->timestamps();
		});
	}
}

database\migrations\2017_01_14_000002_create_oauth_personal_access_clients_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateOauthPersonalAccessClientsTable extends Migration
{
	/**
	 * Run the migrations.
	 *
	 * @return void
	 */
	public function up()
	{
		Schema::create('oauth_personal_access_clients', function (Blueprint $table) {
			$table->bigInteger('id');
			$table->bigInteger('client_id')->index();
			$table->timestamps();
		});
	}
}

database\migrations\2017_01_14_000003_create_oauth_access_tokens_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateOauthAccessTokensTable extends Migration
{
	/**
	 * Run the migrations.
	 *
	 * @return void
	 */
	public function up()
	{
		Schema::create('oauth_access_tokens', function (Blueprint $table) {
			$table->string('id', 100)->primary();
			$table->integer('user_id')->index()->nullable();
			$table->bigInteger('client_id');
			$table->string('name')->nullable();
			$table->text('scopes')->nullable();
			$table->boolean('revoked');
			$table->timestamps();
			$table->dateTime('expires_at')->nullable();
		});
	}
}

database\migrations\2017_01_14_000004_create_oauth_auth_codes_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateOauthAuthCodesTable extends Migration
{
	/**
	 * Run the migrations.
	 *
	 * @return void
	 */
	public function up()
	{
		Schema::create('oauth_auth_codes', function (Blueprint $table) {
			$table->string('id', 100)->primary();
			$table->integer('user_id');
			$table->bigInteger('client_id');
			$table->text('scopes')->nullable();
			$table->boolean('revoked');
			$table->dateTime('expires_at')->nullable();
		});
	}
}

database\migrations\2017_01_14_000004_create_oauth_refresh_tokens_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateOauthRefreshTokensTable extends Migration
{
	/**
	 * Run the migrations.
	 *
	 * @return void
	 */
	public function up()
	{
		Schema::create('oauth_refresh_tokens', function (Blueprint $table) {
			$table->string('id', 100)->primary();
			$table->string('access_token_id', 100)->index();
			$table->boolean('revoked');
			$table->dateTime('expires_at')->nullable();
		});
	}
}

How to Implement Client Model Observer for Laravel Passport Custom IDs.txt

This Gist provides an example of how to implement a Client Model Observer for Laravel Passport. 

This Observer will allow you to intercept the creation of a `Laravel\Passport\Client` model and set a custom id for it.
However, to implement this, you will need to handle the migrations yourself. In my case, the custom ID will be a random, large integer. So the database migrations set the `id` field to a type of `bigInteger`.

Take a look at this complete Gist carefully and implement it yourself. It's very easy.